Fluid pressure machines

ABSTRACT

In a radial, multi cylinder fluid pressure machine, adverse mechanical and/or fluid loads occurring during running are minimised by fluid pressure. The capacity of the machine is selectable by provision of a plunger sleeve and an inner plunger in each cylinder bore, and by valve means selectively controlling their operation so that they can work concurrently or the inner plunger works alone. The adverse loads are minimised by appropriate fluid pressure exerted at opposite ends of the working plungers.

United States Patent 11 1 Harris June 4, 1974 [54] FLUID PRESSUREMACHINES 2,967,490 [/1961 Von Soden 417/487 3,030,932 4 1962 M 11 91 498[75] Inventor: Bruce Hams Bremwmd, 3,199,469 8l1965 Bu sh et al. 91l494England 3,777,624 12/1973 Dixon 91/488 [73] Assignee: HydrostaticTransmission Limited,

[22] Filed: June 18, 1973 [2]] Appl. No.: 370,846

[57] ABSTRACT [30 Foreign Application p i i Data In a radial, multicylinder fluid pressure machine, ad-

June 20 1972 Great Britain 28765/72 verse mechanical and/or fluid loadsoccurring during running are minimised by fluid pressure. The capacity[52 us. c1. 91/488 of the machine is Selectable by Pmvisio" of aPlungfir [51] Im- CL F) 13/06 sleeve and an inner plunger in eachcylinder bore, and [58] Field of 'i; /486 488 by valve means selectivelycontrolling their operation '4l7/2l4 so that they can work concurrentlyor the inner 3 plunger works alone. The adverse loads are minimised 56]References Cited by appropriate fluid pressure exerted at opposite endsUNITED STATES PATENTS of the wmkmg plungers' 2,650.543 9/1953 Pauget417/214 8 Claims, 8 Drawing Figures 7 '82 Z2) /7 14 M II I9 22 1 /8 2 7775 4139 Q 5 24 52 55 55 5 37 55 LE 4240 /0 6 I W W 78 England PrimaryExaminer-William L. Freeh Attorney, Agent, or FirmShapiro & ShapiroFLUID PRESSURE MACHINES This invention relates to fluid pressuremachines by which I mean hydraulic or gas motors or pumps, the motorsand pumps having stationary housings and rotary shafts or rotaryhousings and stationary shafts.

More particularly the present invention relates to a fluid pressuremachine comprising a shaft, a block havin g a main bore by which it issupported on a cylindrical surface for rotation relative thereto aboutan axis eccentric to the shaft axis, a housing or ring coaxial with theshaft and surrounding the block, the shaft being formed or adapted tomaintain a fixed angular relationship between itself and the cylindricalsurface or the housing or ring, the block being formed with boresradially directed from its rotation axis and equispaced in a commonplane normal to the rotation axis of the block and extending from mainbore to the block periphery to provide cylinders containing plungers fordriving the machine, thrust pads formed or secured to and the plungersleeves when working concurrently, can be minimised by opposing fluidpressure.

Mechanical loads on the thrust pads may thus be opposedwhen the innerplungers are working alone and when they are working concurrently withthe plunger sleeves. So also may fluid pressure, which is exerted on thecylindrical surface by the reaction of the inner plungers when workingalone, and of the inner plungers and the plunger sleeves when workingconcurrently, be

opposed by corresponding fluid pressure supplied to the cylindricalsurface.

the housing or ring interior equispaced in a manner thrust directly orindirectly from the plungers and a fluid pressure supply passage andexhaust passageopening on opposite parts of the cylindrical surfacewhich supports the block, whereby communication between each cylindercan be established cyclically with the supply and exhaust passages insequence during relative rotation between the block and cylindricalsurface supporting it, outward thrust on the plunger due to admission offluid pressure thereto in sequence causing driving thrust on thecylindrical surface supporting the block, and eccentric motion of therotation axis of the block relative to the shaft axis. Such a machine ishereinafter referred to as a fluid pressure machine as hereinbeforespecified.

It is customary to supply working fluid at pressures of several tons persquare inch to such'a motor. Adverse mechanical and/or fluidloads whichsuch fluid can engender can be taken care of in thedesign stage of themotor by making load-bearing parts, such as shaft bearings,correspondingly massive.

An object of I the invention is to provide a dualvolume cylindercapacity machine in which the adverse loading mentioned above can bekept below an objectionable level at whichever capacity the machine isrunning. It will be appreciated that it would be possible to The presentinvention deals with the adverse loading in a different manner andresides in a fluid pressure machine as hereinbefore specified, in whichthe effective cylinder capacity is selectable, each cylinder borecontaining a plunger in the form of a sleeve surrounding an innerplunger slidable relatively to the plunger sleeve, and a seal interposedcapable of mutually isolating their effective areas, and in which valvemeans and openings are provided by which working fluid is admissible toeach cylinder bore and which are so arranged that the working fluid canbe admitted to one or to both of the areas in each cylinder bore, andthat adverse mechanical and/or fluid loads attributable to the innerplungers when they are working alone, and attributable to them Thefollowing is a description, by way of example, of certain embodiment ofthe present invention, reference being made to the accompanyingdrawings, in which:

FIGS. 1 and 2 are axial sections at of one form of dual capacity,5-cylinder, hydraulic motor, the inner plungers, however, being indifferent phases;

FIGS. 3 is an end view partly in section of FIG. 1 on line Ill-III ofthe latter Figure but showing the outer plungers in phase with the innerplungers;

FIG. 4 is a diagram of the hydraulic circuit for operating the motor;

FIGS. 5 and 6 are fragments of sections of modified constructions viewedas in FIG. 1;

FIGS. 7 and 8 show views of simplied axial section and end view, partlyin section, of an alternative form of the motor.

Referring particularly to FIGS. 1 and 2, the motor 10 comprises a shaft11 with an eccentric 12 formed between its ends, the shaft beingsupported on taper roller bearings 13 adjacent opposite faces of theeccentric 12 in a casing 14, which is also shown in FIG. 3. A block 15formed with a central or main bore 16 is supported on the eccentric forrotation, a part of the housing or casing 14 in the form of a ring 17being coaxial with the shaft 11 and surrounding the block 15. Thearrangement described preferably includes an Oldham coupling 77 tomaintain the angular relationship between the block 15 and the pads 20.

The block is formed with five bores 18 (only three of which are shown inFIG. 3) radially directed from the rotation axis of the block andextending from the main bore 16 to the block periphery 19 to provide themotor cylinders. These bores 18 or cylinders are equispaced in a commonplane normal to the rotation axis of the block.

Secured to the interior of the ring 17 and equispaced in a mannercorresponding to the bores 18 are thrust pads20, which, as can be seenin FIG. 3, each have a face normal to a radius of the ring 17.

Each of the bores 18 contains a plunger 21 in the form of a sleeve whichsurrounds and supports an inner plunger sleeve 21. Each plunger 21, 22is formed at its inner end with a groove 23 containing a piston ring 24whereas its outer end is reduced externally at 25 to reduce the bearinglength of the plunger and allow it to align itself with the pad andcompensate for manufacturing errors. The plunger sleeve 21 is plain atits outer end face 81 for bearing directly and sealing on a film of themotive fluid on the associated thrust pad 20 or indirectly by a slipperpad, not shown. The inner plunger 22 on the other hand is slightlyrecessed centrally at 26 to provide a sealing land 82 for bearingdirectly or by the slipper on the flim of fluid on the pad 20.

The motor has two possible capacities. As later described, both plungers21, 22 in each bore 18 are employed when the motor is running at fullcapacity (FIG. 3) but only the inner plungers are employed for partialcapacity running (FIGS. 1 and 2).

The inner plunger 22, as shown, has a shaped interior but provided itincludes a through passage the interior could otherwise be solid. Asshown,'the through passage includes a conical surface 27. The effectivearea of the inner plunger 22 therefore consists in the surface 27 and anannular face 28 at its inner end.

The effective area of the plunger sleeve 21 consists in an annular face29 at its inner end.

Thus for the full capacity running, the effective area is contributed bythe faces 27, 28, 29; for the partial capacity running, the faces 27, 28only.

The plunger sleeve 21 has an internal lip 30 on which pressure liquid inthe working space 31 below the inner plunger 22 can react as laterdescribed to retain the sleeve 21 in an inoperative position for thepartial capacity running.

The inner end of each bore 18 contains an annular seal the precise formof which is not important. As shown, the seal is a formationconveniently in the form of a disc 32 inset in the block 15. The upperface of the disc 32 is formed with a central boss 33 providing in thiscase an external frusto-conical seating 34 against which the plungersleeve 21 can seal by contact with a peripheral edge 35 of the lip 30when the plunger sleeve 21 is inoperative.

The disc 32 is formed with a central opening 36 and openings 37 in itsmargin. The central opening 36 can admit pressure liquid directly to theworking space 31. The openings 37 in the disc margin can vent or admitliquid to a space 38 below the face 28 of the plunger sleeve 21.

Pressure liquid for driving the plungers 21, 22 can be circulated from asupply through the motor by screwthreaded ports 39, 40 (FIGS. 1 and 2)located towards one end of the casing 14, the direction of circulationdetermining the sense of rotation of the shaft 11, supposing the casing14 is held stationary. These ports are in constant communication withrespective annular grooves 41, 42 inside the casing 14. The grooves 41,42 communicate with respective passages 43, 44 extending longitudinallythrough part of the shaft 11 and eccentric 12. At one end the passagesterminate in short radial portions 45, 46 which are oppositely directedand open into respective grooves 47, 48 in the surface of the eccentric12, and thence by bores 49, S0 in the block to the central opening 36 ofthe respective discs 32. At the other end the passages 43, 44 terminateat the left hand end of the shaft 11 in FIGS. 1 and 2 at a valve block52 enclosed by an extension 52 of the casing 14 and rotating with theshaft 11.

The block 51 is formed with waisted bores 53, 54 aligned with therespective passages 43, 44. These bores 53, 54 contain check valves,comprising waisted spools 55, 56 respectively, operation of whichcontrols venting and pressurising of the space 38 below each of theplunger sleeves 21 and thereby whether the motor is arranged for thefull or partial capacity running. The spools 55, 56 are normallyspring-urged to the left in FIGS. 1 and 2 but are displaceable againstthe spring pressure by a plunger 57 which is slidable to the right in arecess 58 at the outer end of the block 51 by the admission of pressurefluid into the extension 52 through a screwthreaded port 59.

The spools 55, 56 normally seal on corresponding seatings 60, 61 underspring pressure and are held off the seatings 62, 63. Inward movement ofthe plunger 57 reverses the condition, the spools 55, 56 becoming heldoff the seatings 60, 61 and sealed on the seatings 62, 63.

The waisted part of the bore 53 communicates with a pair of grooves 64extending in the eccentric 12 parallel with and on each side of thegroove 47 at a position where, druing part of a 360 rotation of theshaft 11 relative to the casing 14, the grooves 64 communicate with theopenings 37 in the margin of the disc 32 as in FIG. 1. The communicationbetween the bore 53 and openings 37 is by bores 65 to 67, grooves 64,and bores 68 in the block 15, there being two bores 67, which areparallel branches of the bore 66.

Similarly during part of a 360 rotation of the shaft 11, the waistedpart of the bore 54 communicates with a pair ofgrooves 69 in theeccentric 12 in planes parallel with and'on each side of a radial planecontaining the groove 48 through bores 70 to 72. The grooves communicatewith bores 73 in the block 15 and thence with the openings 37 in thedisc 32.

The eccentric 12 is also formed with a pair of circumferential grooves164 in planes parallel with the planes containing the grooves 68, 69 butfurther removed than them from the grooves 47, 48.

When the spools 55, 56, are being held off the seatings 62, 63 by springpressure the waisted parts of the bores 53, 54 communicate with ductingor a recess 74 in the inner end of the plunger 57. The ducting or recess74 is permanently open to a bore 75 extending from the left hand end(FIG. 1) of the shaft 11 along the rotation axis, and intersecting abore 76 which vents past the tapered rollers 13 into the casingenclosure and out through a port or sump hole 78 in the casing 14.

Assuming that the parts of the motor are in the relative positions showninFIG. 1, the spools 55, 56 engage the seating 60, 61 (FIG. 4),rendering the motor set for the partial capacity running. The groove 47will be communicating simultaneously with the central opening 36 of eachdisc 32 within the three cylinders 18 above the equivalent of thehorizontal diameter of the ring 17 shown in FIG. 3, that Figure howeverrelating to full capacity running, whereas the groove 48 will becommunicating in a corresponding manner with the two cylinders 18 belowthat diameter. Thus, liquid forced in the motor from the port 39 andarriving by the groove 41 and passages 43, 45 at the groove 47 willenter respective working spaces 31 below the inner plungers 22 in thefirst three cylinders .mentioned through the bores 49 and openings 36whereas liquid in the other-two cylinders will exhaust through theopenings 36 and bore 50 into the groove 48 and out through thepassage 44groove 42 and port 40.

The ensuing displacement cycle of the plungers 22 corresponds to thatindicated in FIG. 3 and later described. Whilst the spools 55, 56 engagethe seatings 60, 61, however, the plunger sleeves 21 remain inoperative,the hydraulic pressure in the spaces 31 acting on the inner radialsurfaces of the lips 30, thereby holding the edges 35 of the lips insealing contact with the seatings 34 and isolating the spaces 38 belowthe plunger sleeves 21 from the spaces 31.

Whilst the spaces 31 are isolated from the spaces 38, the spaces 38 arevented to the sump hole 78 through the bores 37, 68, grooves. 64, bores67 to 65, past the seating 62 in the valve bore 53, through the recess74 and bores 75, 76 to the hole 78, and correspondingly through thebores 37, 73 channels 69 bores 72 to 70, past the seating 63 in thevalve bore 54, through the recess 74 and to the hole 78.

To set the motor for full capacity running, hydraulic or other pressureis applied to the plunger 57 to displace it inwardly (to the right inFIGS. 1 and 4) to cause the spools 55, 56 to seal against the seatings62, 63, respectively, and unseal from seatings 60, 61. The spaces 38 arethereby subjected to hydraulic pressure in the passages 43, 44; frompassage 43 bore 53, past seating 66, through bores 65 to 67, groove 64and bores 68, 37 to the spaces 38, and correspondingly from passage 44,bore 54, past seating 61, through bores 70 to 72, grooves 69, bores 73,37 to spaces 38.

The plunger sleeves 21 will then be displaced in phase with theircompanion inner plungers 22, engagement being maintained between theinner radial face of the lip 30 and the inner end face of the innerplunger 22 in each case.

The longitudinal dimensions of the plunger sleeves 21 and inner plungers22 are such that in each case, whilst the engagement of the lip 30 ismaintained, the outer end of plunger sleeve 21 bears on the filmofliquid on the corresponding pad 20. a

The land 82 of the inner plunger 22 presents an area such that, when themotor is running at partial capacity, the land 82 is supported on thefilm of liquid on the pad 20, which is replenished by outward radialflow from the crown recess 36 under hydraulic pressure from the innerend of the plunger 22. Similarly the end face 81 on the plunger sleeve21 presents an area such that, when the motor is running at fullcapacity, the liquid film on the pad 20 supports the face 81. Thus,whether the motor is running at partial or full capacity, the outwardmechanical loading imposed by the outer ends of the inner plungers 22,and of the inner plungers and plunger sleeves 21, respectively, isbalanced by the opposing hydraulic pressure of the liquid film on thepads 20.

FIG. 3 illustrates the displacement cycle of the plungers 21, 22laterally in relation to the thrust pads 20 during full capacityrunning. However, it will be appreciated that the inner plungers 22 willmove in a corresponding cycle during partial capacity running. Forconvenience, only the inner plungers 22 have been marked A to E and willbe referred to in the description of the cycle. Plunger A is at thebeginning of its outward power stroke, plunger C almost at the end ofits power stroke and plunger B is in an intermediate position. PlungersD and E are returning on their exhaust strokes. Correspondingly, theaxes of the plungers A and C are displaced somewhat in the clockwisedirection (FIG. 3) with respect to the centres of the corre-- spondingthrust pads 20 whereas the axis of the plunger B is at maximumdisplacement in this direction. The axes of the plungers D and E on theother hand are displaced in an anti-clockwise direction with respect totheir thrust pad centres. 1

It will be observed that the lines of action through the plungers A to Eall pass through the centre of the eccentric. This arrangement minimisestorque on these plungers.

The motive liquid in driving the plungers A, B, C outwardly, reacts onthe eccentric 12, thereby displacing its centre and the block 15 awayfrom the corresponding thrust pads 20, the displacement due to theplunger C being the greatest of the three since it is almost at the endof its power stroke. The eccentric 12 thereby derives clockwise rotation(FIG. 3) about the shaft axis and imparts a corresponding eccentricmotion to the rotation axis of the block 15.

The rotation of the eccentric 12 causes the motive liquid to be fed insequence to all of the cylinders and exhausted in sequence in arepetitive cycle.

Fluid pressure is exerted on the eccentric by reaction of theinnerplungers 22 when the motor is running at partial capacity. Thispressure is opposed by corresponding pressure of motive fluid suppliedto the surface of the eccentric 12 by the grooves 47, 48. In this manneritis possible to balance hydraulically forces which would otherwise loadthe shaft and block 15. Similarly, when the motor is running at fullcapacity, fluid pressure'exerted on the eccentric 12 by reaction of theinner plungers 22 and the plungers sleeves 2] is opposed andhydraulically balanced by corresponding motive fluid pressure suppliedto the surface of the eccentric 12 by the grooves 47, 48, 64 and 69. Ineach mode of running, there is a degradation of fluid pressure from thegrooves 47, 48 outwards along the eccentric in both directions. Inpartial capacity running the degradation extends to the grooves 64, 69;in full capacity running grooves 47, 48, 64 and 90 are being supplied bymotive fluid, and the degradation of the fluid pressure extends to thecircumferential grooves 164.

It will be appreciated that if the casing 14 (inclusive of the ring 17)is held stationary, the shaft 11 provides the output, but if the shaftis held stationary the casing provides the output.

When the motor is put to use as a pump, input is by way of the shaft orthe casing, and the casing or shaft is held stationary as appropriate.

. The modifications shown inFIGS. 5 and'6, respectively, involvingplungers and the eccentric, and shown in FIGS. 7 and 8 involving a motoror pump arangement, also concern dual-volume cylinder capacity machines.Both such machines work in a manner analogous to the motor alreadydescribed and involve oppos- I views inFIGS. 5 and 6 and the section inFIG. 2.

As to modifications, it will be noted that the plunger sleeve 21 in FIG.5 is formed with a passage or bore 83 for pressure communication betweenthe inner end 28 and the bottom of a recess 84 at a lipped outer end,which accommodates a lipped outer end of the inner plunger 22. Suchcommunication ensures a faster, more positive response of the sleeve 21between its operative position and its inoperative position when changeis made either way between partial and full capacity running.

The seal formation 132 at the inner end of the sleeve 21 includes acylindrical boss 85 incorporating a sealing member 86, for contact withthe inner cylindrical surface of the lip 30 when the sleeve isinoperative.

Furthermore, the grooves 64 are subdivided into two short pairs, themembers of which are fed or vented by suitably branched bores 67. Thecounterparts of the grooves 69 and bores 72 (not shown in FIG. 5) aremodified in a manner analogous to the grooves 64 and bores 67 in FIG. 5.Such subdivision of the grooves 64 and 69 is to provide a structuraldifference which influences the fluid pressure available at the surfaceof the eccentric 12 for opposing adverse reaction pressure exerted bythe plunger sleeve 21 whenoperative.

In FIG. 6 a thinner annular disc 231 set in a corresponding recess inthe block replaces the disc 32 of the earlier Figures. The disc 231surrounds and holds the inner end of a tube 232 which is open at bothends. The passage by which fluid pressure is communicated betweenopposite ends of the inner plunger 22 is of larger radial dimensions atits inner end than at its outer end.

The inner end of the plunger 22 throughout the plunger stroke surroundsthe tube 232 which serves to deliver working fluid to the inside of theinner plunger 22. The tube 232 and plunger 22 are mutually spaced toform between them a passage which maintains communication between themouth of the tube 232 and an inner radial face of the lip 30 of theplunger sleeve 21.

The purpose of the tube 232 is to ensure that, when the passages 68 arevented, the fluid pressure supplied by the passage 36 acts on the innerradial face of the lip 30 and the plunger sleeve 21 to seal, by means ofthe lip 30, against the disc 231.

FIG. 6 also shows sealing rings 233 arranged in circumferential grooves234 formed in the eccentric 12 on each side of the grooves 47 andbetween the grooves 64 and the end faces of the eccentric.

The five cylinder dual-capacity hydraulic motor shown diagrammaticallyin FIGS. 7 and 8 corresponds in some degree with the motor describedwithreference to FIGS. 1 to 4, and corresponding reference numerals areused on corresponding parts. Thus, the counterpart of the shaft 11 issupported on bearings 13 at one end ofa casing 90 which is coaxial withthe shaft 11 and encloses the motor. The counterpart of the eccentric 12is provided by a stub shaft 91 secured to the other end of the casing90, the longitudinal axis of the stub shaft 91 being eccentric to theaxis of shaft 11.

The shaft 11 is adapted by means of a housing 92 to provide thecounterpart of the ring 17. The ring 17 surrounds a cylinder block 15which is mounted for rotation by means ofa central bore 16 on the stubshaft 91.

The lines of action of plunger sleeves 21 and inner plungers 22supported by the block 15 pass through the longitudinal axis of the stubshaft.

The motor includes an hydraulic circuit corresponding to FIG. 4 but forsimplicity only the passages 43, 44, groove 47 and discs 32 have beenshown in FIGS. 7 and 8.

When pressure liquid is circulated through supply and exhaust passages43, 44 in the stub shaft 91, the action of the plungers 22 or 21 and 22,depending on whether the hydraulic circuit is set for partial or fullcapacity running of the motor, corresponds to that of the plungers inthe motor in FIGS. 1 and 2 or FIG. 3. The pressure driving the plungers22 (or 21, 22) outwardly in FIG. 8 reacts on the stub shaft 91,displacing its centre and the block 15 away from the thrust. Therotation axis of the block 15 is moved eccentrically relative to theaxis of the shaft 11 whereas the casing 90 is rotated on that axis.

The spools 55, 56 could be operated pneumatically, mechanically orelectrically instead or hydraulically. They could also be cylindricalspool valves or any other type of hydraulic control valve. They couldalso be arranged to operate automatically depending upon the operatingpressure of the motor (or pump), such that if the pressure increases toa pre-set level during partial capacity running, the running wouldautomatically change to full capacity. Similarly, when the operatingpressure falls to a pre-set minimum during full capacity running, itwould automatically change to partial capacity running.

I claim:

1. A fluid pressure machine comprising a structure carrying a housing,and a shaft providing a surface eccentric with respect to the housingand surrounded thereby, bearings arranged on the structure to permitrelative rotation between the housing and the shaft, a block'having amain bore by which the block is borne by the eccentric surface forrelative rotation thereto,

1 the block being surrounded by the housing and having.

a circular array of radially-directed cylinder bores provided therein, aplunger in the form of a sleeve in each cylinder bore and an innerplunger surrounded and slidably supported by the plunger sleeve,-theplunger sleeve and inner plunger by their arrangement in theradially-directed cylinder bore in the block being intermediate thehousing and the eccentric surface for transmitting relative motiontherebetween, the plunger sleeve and inner plunger each having arespective effective area for drivingly interacting with motive fluid, aseal interposed between the plunger sleeve and the inner plunger capableof mutually isolating their respective effective areas in the cylinderbore, each cylinder bore and the block being formed with openings forpassage of the motive fluid to and from the respective areas, the shafthaving inlet and outlet passages communicating with correspondingopenings in the eccentric surface, and cyclically communicable with therespective openings in the block and each cylinder bore in each relativerotation between the eccentric surface and the block, a supply of motivefluid connected to the shaft inlet passage, and valve means arranged toselect the effective cylinder capacity of the machine by controllingpassage of the motive fluid to and from the openings in each cylinderand thereby operation of the seal, transfer of the motive fluid to oneand to both of the effective areas in each cylinder correspondingrespectively to partial capacity and full capacity running of themachine, there being fluid pressure existing between the eccentricsurface and the block, and between the housing and the inner plungersand plunger sleeves during the partial and full capacity runningrespectively, acting in opposition to and minimising mechanical andfluid loads attributable, respectively, to the inner plungers whenworking alone, and when working concurrently with the plunger sleeves.

2. A fluid pressure machine according to claim 1, in which each innerplunger and plunger sleeve has an inner end adjacent the eccentricsurface and an outer end adjacent the housing, and a formation isprovided having a central opening arranged in each cylinder bore betweenthe inner end of the plunger sleeve and the opening in the block, theopening in the formation communicating with the opening in the block andwith the inner end of the inner plunger, and the formation having aperiphery against which the inner end of the plunger sleeve can seal andthereby mutually isolate the respective effective areas of the plungersleeve and inner plunger; and in which the plunger sleeve has at itsinner end an internal lip with an internal radial face on which pressurefluid can act and urge the plunger sleeve into sealing contact with theperiphery of the formation when the valve means is operating to admitthe fluid to the inner plunger to the exclusion of the plunger sleeve,and furthermore is formed with a passage of larger radial dimension atthe inner end of the inner plunger than itsouter end, a tube having aninner end carried in the opening in the block to each cylinder bore andhaving an outer end extending into the larger radial dimensioned portionof the passage in the inner plunger throughout the stroke of the innerplunger but being radially spaced therefrom, thereby maintainingcommunication between the outer end of the tube and the inner radialface of the plunger sleeve lip.

3. A fluid pressure machine according to claim 1, in which each innerplunger and plunger sleeve has an inner end adjacent the eccentric andan outer end adjacent the housing, and a formation is provided having acentral opening arranged in each cylinder bore between the inner end ofthe plunger sleeve and the opening in the block, the opening in theformation communicating with the opening in the block and with the innerend of the inner plunger, and the formation having a periphery againstwhich the inner end of the plunger sleeve can seal and thereby mutuallyisolate the respective effective areas of the plunger sleeve and innerplunger.

4. A fluid pressure machine according to claim 3, in which the plungersleeve has at its inner end an internal lip with an internal radial faceon which pressure fluid can act and urge the plunger sleeve into sealingcontact with the periphery of the formation when the valve means isoperating to admit the fluid to the inner plunger to the exclusion ofthe plunger sleeve.

5. A fluid pressure machine according to claim 1, in which each innerplunger is of a form permitting communication of fluid pressure betweenopposite ends of the inner plunger.

6. A fluid pressure machine according to claim 5, in which each innerplunger has an inner end adjacent the eccentric surface and an outer endadjacent the housing, and the outer end has a central recess surroundedby a peripheral land.

7. A fluid pressure machine according to claim 5, in which each plungersleeve has at its inner end an internallip with an internal radial face,each inner plunger is formed with a passage of larger radial dimensionat the inner end of the plunger than at its outer end, and a tube isprovided having an inner end carried in the opening in the block to eachcylinder bore and having an outer end extending into the larger radialdimensioned portion of the passage in the inner plunger and surroundedthereby throughout the stroke of the inner plunger but being radiallyspaced therefrom, thereby maintaining communication between the outerend of the tube and the plunger sleeve lip.

8. A fluid pressure machine according to claim 5, in which the outer endof the inner plunger has a peripheral lip, the outer end of the plungersleeve is formed with a recess having a bottom corresponding to the lipon the inner plunger for receiving the same, and with a passagepermitting communication of fluid pressure between opposite ends of theplunger sleeve, such communication with the outer end of the plungersleeve being made with the bottom of the recess.

. l l= =l

1. A fluid pressure machine comprising a structure carrying a housing,and a shaft providing a surface eccentric with respect to the housingand surrounded thereby, bearings arranged on the structure to permitrelative rotation between the housing and the shaft, a block having amain bore by which the block is borne by the eccentric surface forrelative rotation thereto, the block being surrounded by the housing andhaving a circular array of radially-directed cylinder bores providedtherein, a plunger in the form of a sleeve in each cylinder bore and aninner plunger surrounded and slidably supported by the plunger sleeve,the plunger sleeve and inner plunger by their arrangement in theradially-directed cylinder bore in the block being intermediate thehousing and the eccentric surface for transmitting relative motiontherebetween, the plunger sleeve and inner plunger each having arespective effective area for drivingly interacting with motive fluid, aseal interposed between the plunger sleeve and the inner plunger capableof mutually isolating their respective effective areas in the cylinderbore, each cylinder bore and the block being formed with openings forpassage of the motive fluid to and from the respective areas, the shafthaving inlet and outlet passages communicating with correspondingopenings in the eccentric surface, and cyclically communicable with therespective openings in the block and each cylinder bore in each relativerotation between the eccentric surface and the block, a supply of motivefluid connected to the shaft inlet passage, and valve means arranged toselect the effective cylinder capacity of the machine by controllingpassage of the motive fluid to and from the openings in each cylinderand thereby operation of the seal, transfer of the motive fluid to oneand to both of the effective areas in each cylinder correspondingrespectively to partial capacity and full capacity running of themachine, there being fluid pressure existing between the eccentricsurface and the block, and between the housing and the inner plungersand plunger sleeves during the partial and full capacity runningrespectively, acting in opposition to and minimising mechanical andfluid loads attributable, respectively, to the inner plungers whenworking alone, and when working concurrently with the plunger sleeves.2. A fluid pressure machine according to claim 1, in which each innerplunger and plunger sleeve has an inner end adjacenT the eccentricsurface and an outer end adjacent the housing, and a formation isprovided having a central opening arranged in each cylinder bore betweenthe inner end of the plunger sleeve and the opening in the block, theopening in the formation communicating with the opening in the block andwith the inner end of the inner plunger, and the formation having aperiphery against which the inner end of the plunger sleeve can seal andthereby mutually isolate the respective effective areas of the plungersleeve and inner plunger; and in which the plunger sleeve has at itsinner end an internal lip with an internal radial face on which pressurefluid can act and urge the plunger sleeve into sealing contact with theperiphery of the formation when the valve means is operating to admitthe fluid to the inner plunger to the exclusion of the plunger sleeve,and furthermore is formed with a passage of larger radial dimension atthe inner end of the inner plunger than its outer end, a tube having aninner end carried in the opening in the block to each cylinder bore andhaving an outer end extending into the larger radial dimensioned portionof the passage in the inner plunger throughout the stroke of the innerplunger but being radially spaced therefrom, thereby maintainingcommunication between the outer end of the tube and the inner radialface of the plunger sleeve lip.
 3. A fluid pressure machine according toclaim 1, in which each inner plunger and plunger sleeve has an inner endadjacent the eccentric and an outer end adjacent the housing, and aformation is provided having a central opening arranged in each cylinderbore between the inner end of the plunger sleeve and the opening in theblock, the opening in the formation communicating with the opening inthe block and with the inner end of the inner plunger, and the formationhaving a periphery against which the inner end of the plunger sleeve canseal and thereby mutually isolate the respective effective areas of theplunger sleeve and inner plunger.
 4. A fluid pressure machine accordingto claim 3, in which the plunger sleeve has at its inner end an internallip with an internal radial face on which pressure fluid can act andurge the plunger sleeve into sealing contact with the periphery of theformation when the valve means is operating to admit the fluid to theinner plunger to the exclusion of the plunger sleeve.
 5. A fluidpressure machine according to claim 1, in which each inner plunger is ofa form permitting communication of fluid pressure between opposite endsof the inner plunger.
 6. A fluid pressure machine according to claim 5,in which each inner plunger has an inner end adjacent the eccentricsurface and an outer end adjacent the housing, and the outer end has acentral recess surrounded by a peripheral land.
 7. A fluid pressuremachine according to claim 5, in which each plunger sleeve has at itsinner end an internal lip with an internal radial face, each innerplunger is formed with a passage of larger radial dimension at the innerend of the plunger than at its outer end, and a tube is provided havingan inner end carried in the opening in the block to each cylinder boreand having an outer end extending into the larger radial dimensionedportion of the passage in the inner plunger and surrounded therebythroughout the stroke of the inner plunger but being radially spacedtherefrom, thereby maintaining communication between the outer end ofthe tube and the plunger sleeve lip.
 8. A fluid pressure machineaccording to claim 5, in which the outer end of the inner plunger has aperipheral lip, the outer end of the plunger sleeve is formed with arecess having a bottom corresponding to the lip on the inner plunger forreceiving the same, and with a passage permitting communication of fluidpressure between opposite ends of the plunger sleeve, such communicationwith the outer end of the plunger sleeve being made with the bottom ofthe recess.